The Siege of Jerusalem occurred from September 20 to October 2, 1187 which resulted in the near total breakdown of the crusader Kingdom of Jerusalem and the regain of Jerusalem by Saladin. Provoking the Third Crusade by allowing its primary goal to return Jerusalem to Christendom.

On July 4 1187, the Kingdom of Jerusalem was completely overthrown at the Battle of Hattin. Saladin took over Acre, Jaffa, Nablus, Sidon, Toron, Ascalon and Beirut. Other refugees and survivors of the battle escaped to Tyre, which was the only city able to maintain strength against Saladin. Balian of Ibelin had asked Saladin for safe passage to Jerusalem to allow him to retrieve Maria Comnena his wife and their family. This request was granted by Saladin, upon terms that Balian not to remain in Jerusalem or take up arms against him. Patriarch Heraclius, Queen Sibylla and the rest of the settlers begged him to take charge to guard the city.

Heraclius then argued that he must remain for the sake of Christianity and offered to exempt him of the oath, in Balian agreed upon. The decision was presented to Saladin at Ascalon via a group of representatives of burgesses, who denied the sultans proposals for a discussed surrender of Jerusalem. Saladin then made arrangement for an chaperon to accompany his wife, children and entire household to Tripoli.

The situation in Jerusalem was grim. The city was filled with refugees escaping Saladin's conquests. There were less than fourteen knights in the entire city so sixty new squires were created from the burgesses and knights in training. The armies of Egypt and Syria were assembled under Saladin and after a short and failed siege of Tyre, the sultan arrived outside Jerusalem on September 26. It is believed that the sultan rounded up the remaining Muslim soldiers whom had survived at the Horns of Hattin, along with several thousand troops from Egypt and Syria. Saladin favoured to take the city without bloodshed, but those inside the city vowed to destroy it till the death rather than handing it over peacefully and the siege began.

Saladin moved his camp on September 26 to the Mount of Olives from where there was no major wall from which the reformers could counter attack. A portion of the wall collapsed on September 29 through the constant siege of attack.Balian rode out at the end of September with an embassy to meet with the Sultan, offering the surrender that had been refused. Balian finally agreed that the city would be handed over to Saladin peacefully.

The keys to the Tower of David were handed over by Balian on October 2. Those that were forced into slavery were freed through Saladin's generosity. Balian and Heraclius freed many with their own money and even offered themselves as hostages for the remaining several thousand citizens whose ransoms had not been paid. Saladin refused this offer and allowed for a march from Jerusalem. Balian was allowed to join his wife and family in Tripoli. Heraclius evacuated a number of church treasures and containers for relics which brought scandal to the Muslim chronicler Imad ad-Din al-Isfahani.